An Experimental Investigation of the Gas Permeability of Tectonic Coal Mineral under Triaxial Loading Conditions

Zhaoying Chen,Junhui Wang,Qingling Tian,Hongwei Zhang,Yi Wang,Mingbo Chi,Guofu Li,Zemin Li

doi:10.3390/min12010070

Zhaoying Chen, Junhui Wang + Show 6 more

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https://doi.org/10.3390/min12010070

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Abstract

Underground coal mining of CH4 gas-rich tectonic coal seams often induces methane outburst disasters. Investigating gas permeability evolution in pores of the tectonic coal is vital to understanding the mechanism of gas outburst disasters. In this study, the triaxial loading–unloading stresses induced gas permeability evolutions in the briquette tectonic coal samples, which were studied by employing the triaxial-loading–gas-seepage test system. Specifically, effects of loading paths and initial gas pressures on the gas permeability of coal samples were analyzed. The results showed the following: (1) The gas permeability evolution of coal samples was correlated with the volumetric strain change during triaxial compression scenarios. In the initial compaction and elastic deformation stages, pores and cracks in the coal were compacted, resulting in a reduction in gas permeability in the coal body. However, after the yield stage, the gas permeability could be enhanced due to sample failure. (2) The gas permeability of the tectonic coal decreased as a negative exponential function with the increase in initial gas pressure, in which the permeability was decreased by 67.32% as the initial gas pressure increased from 0.3 MPa to 1.5 MPa. (3) Coal samples underwent a period of strain development before they began to fail during confining pressure releasing. After the stress releasing-induced yield stage, the coal sample was deformed and cracked, resulting in a quickly increase in gas permeability. With a further releasing process, failure of the sample occurred, and thus induced rapidly increasing gas permeability. These obtained results could provide foundations for gas outburst prevention in mining gas-rich tectonic coal seams.

Highlights

IntroductionA coalbed methane outburst disaster often threatens the safety mining of coal resources [1,2]
Understanding the gas permeability evolution of tectonic coal is significant for the prevention of gas outburst disasters in coal mining systems
The triaxial gas seepage apparatus was employed to investigate the gas permeability of tectonic coal samples resourced from a Malan coal mine under various stresses, gas pressures and loading–unloading conditions

Summary

Introduction

A coalbed methane outburst disaster often threatens the safety mining of coal resources [1,2]. The original structure of coal, which is affected by tectonism such as faulting, folding and slipping, could be destroyed by tectonic stress, causing the coal to be severely crushed or even pulverized [4]. This severely crushed or pulverized coal is commonly known as tectonic coal or tectonically deformed coal and is widely distributed in southwestern and central-eastern China [3] (Figure 1).

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